Wide Range Of Shear Rates Research Articles

Structural deformation/instability of the co-extrudate rubber profiles due to die swell: Experimental and CFD studies with 3D models

Co-extrusion is one of the most effective processes for manufacturing long polymeric profiles with two textures with different constituent rubber compound’s inherent properties. Typically, two rubber compounds are amalgamated with each other to construct hard and soft surfaces. This study investigates the die swell characteristics while extruding the two rubber components using the proper material properties. Herein, the EPDM rubber-based compound’s thermal and rheological parameters have been identified to predict the extrudate’s overall deformation profiles during the extrusion molding process. Carreau-Yasuda and Arrhenius approximate law exhibited an excellent fit for a wide range of shear rates with the experimental data. Finally, the extrudate’s overall deformation has been simulated using finite element software (ANSYS Polyflow®) at real processing conditions along with the boundary conditions (inlet, die wall, Interfaces, extrudate free surface, profile cross-section). Furthermore, numerical results generated from the simulation have been cross-verified with the experimental results for a complex-shaped rubber profile, and a good agreement with an efficiency of > 98.5% was obtained.

Development and validation of a compression flow model of non-Newtonian adhesives

ABSTRACT In bonding processes, the final distribution of the adhesive in the gap depends on the compressing normal load, velocity and kinematics, the adhesive properties, but above all on the initial adhesive distribution. The latter is also largely responsible for trapped air and the adhesive squeezes out at the edges. A model has recently been developed for the simulation of the flows during compression processes in adhesively bonded joints. This paper extends the aforementioned model towards shear rate-dependent viscosity, a phenomenon crucial for most industrial adhesives. Besides the assumption of a Newtonian fluid, approximations of a power-law and a Yasuda law are used. For this purpose, a further subordinate Newton method for determining the flow profiles is added to the existing model. Rheological measurements over a wide range of shear rates serve as a reference. For the verification, studies are performed on two academic examples: a rectangular, and a circular propagation. The results are compared with analytical solutions and CFD simulations. A very good agreement of pressure (deviations below 1.5%), and velocity profiles (deviations below 5%), for all scenarios and flow laws, was found. The long-term goal of this model development is the prediction of adhesive compression flows for complex application patterns.

A theoretical formulation of dilatation/contraction for continuum modelling of granular flows

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An experimental scaling law for particle-size segregation in dense granular flows

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Rheology of Cohesive Granular Media: Shear Banding, Hysteresis, and Nonlocal Effects

Powders or cohesive granular materials are widely handled in industries. However, our understanding of the rheology of these materials is limited. Here, we provide a comprehensive analysis of the rheology of a cohesive granular medium, sheared in a normal-stress-imposed plane shear cell over a wide range of shear rate, employing numerical simulations. At high imposed shear rates, the flow is homogeneous, and the rheology is well described by the existing scaling laws, involving the inertial number and the effective cohesion number [S. Mandalet al., Insights into the Rheology of Cohesive Granular Media, Proc. Natl. Acad. Sci. U.S.A. 117, 8366 (2020)]. However, at low imposed shear rates, the flow is inhomogeneous, exhibiting the coexistence of flowing and nonflowing regions in the material, popularly known as shear banding. We thoroughly analyze the crucial features of this shear-banded flow regime and discuss striking similarities between the shear banding for granular media and other complex fluids. We reveal that the occurrence of shear banding is related to the existence of a nonmonotonic intrinsic rheological curve and that increasing adhesion increases the nonmonotonicity and the tendency toward shear localization. A simple theoretical model based on a nonlocal rheological model coupled with a nonmonotonic flow curve is proposed and is shown to successfully reproduce all the key features of the shear banding observed in the numerical simulations. The results have important implications for the handling of powders in industries.

Modelling of Flow Behaviour and Rheological Properties of M2 Steel in Semisolid State

The present study develops a model to investigate time dependent behaviours of M2 steel in semisolid state during step-change in shear rate. The Couette flow of the semisolid material between two parallel plates is considered. The flow field is presented by momentum conservation equation. The non-Newtoniun behaviour of the semisolid material is expressed by the Herschel-Bulkley model. The agglomeration and de-agglomeration phenomena of the suspended particles in semisolid state under shear are represented introducing a time dependent structural parameter. The proposed model fitted well with existing work in a wide range of shear rates and could predict the flow and apparent viscosity of semisolid M2 steel. Finally, the work involves prediction of the flow field, rate of strain and apparent viscosity of the semisolid material under transient condition. It is observed that the time dependent viscosity is highly non-linear during step-change in shear rate. It is noticed that the structural parameter decreases as the shear rate is increased. Whereas, the apparent viscosity decreases with increasing shear rate but shows an undulation and after that gradually rises to a higher steady value as the plate velocity decreases suddenly.

Altering and eliminating irreversible shear thickening of fumed silica slurries using spherical silica

Shear thickening behavior in colloidal dispersions occurs at a wide range of shear rates and concentrations. Using a small gap, parallel plate rheology allows access to shear rates up to 200,000 s−1. Fumed silica suspensions exhibited irreversible shear thickening at critical shear rates above 10,000 s−1, which depended strongly on silica concentration. Introducing 10 nm and 110 nm spherical silica particles to 180 nm fumed silica solutions resulted in increasing the critical thickening shear rate along with reducing the magnitude of thickening. The introduction of sufficient spherical particles to the fumed silica solutions via particle addition at 2 wt% or particle replacement at 7 wt% resulted in no shear thickening or formation of agglomerates. Although shear thickening was tuned by varying the concentration and particle size of spherical silica; hysteresis, i.e., the irreversibility of thickening, remained. In addition, rheo-small-angle light scattering measured the formation of agglomerates greater than 1 μm after shear thickening.

Rheological behavior of scCO2-Foam for improved hydrocarbon recovery: Experimental and deep learning approach

CO2 foam as a fracturing fluid for unconventional reservoir has been of huge interest due to its potential in solving various challenges related to conventional water-based fracturing. The rheological property of CO2 foam is a key factor to control the efficiency of fracturing process that is strongly influenced by different process parameters such as foam quality, temperature, pressure, and shear rate. The quantification of these parameters under reservoir conditions leads to the design of optimum injection strategy. However, the traditional modeling approaches are unable to provide fast and accurate prediction while considering combined effect of all these parameters. Here, we proposed a data driven approach based on supervised deep learning to estimate rheological property of CO2 foam as a function of foam quality, temperature, pressure, and shear rate. We exploit deep neural networks (DNNs) that are trained to learn the complex nonlinear aspects of the data. For the data generation, we performed a series of experiments for CO2 foams by varying different process variables. CO2 foams at different qualities were generated using conventional surfactant in a flow loop system and foam viscosity measurements were performed at HPHT under wide range of shear rate. The architecture of DNN was optimized to accurately estimate the foam apparent viscosity for given foam quality, temperature, pressure, and shear rate. The predictive capability of designed network is found to be significantly high, analyzed by regression coefficient approaching unity, low mean squared error, and low average absolute relative deviation (<1.8%). The designed neural network allows robust and accurate prediction of foam apparent viscosity at different foam qualities under various reservoir condition, which demonstrates its practicality for CO2 foam projects for fracturing unconventional reservoirs.

Electrical conductivity under shear flow of molten polyethylene filled with carbon nanotubes: Experimental and modeling

AbstractThis work aims to describe the conductivity evolution of polymer composites (polyethylene filled with carbon nanotubes) during a shearing deformation. Rheo‐electric measurements were carried out to observe the shear‐induced fillers network modification. Extended steady shear forces the conductivity to evolve asymptotically to a steady level attesting to an equilibrium between structuring and break up mechanisms in the melted polymer. Numerous experiments were conducted to cover a wide range of shear rate from 0.05 to 10 s−1 and for carbon nanotubes concentrations between 1.3 and 2.9 vol%. A model is proposed to predict the conductivity evolution under shear deformation using a simple kinetic equation inserted in a percolation law. Structuring parameter was found to be solely dependent on the temperature whereas shear induced modification terms were found to be mostly driven by the shear rate and the fillers content.

Elastic flow instabilities and macroscopic textures in graphene oxide lyotropic liquid crystals

Graphene oxide (GO) forms a well-aligned lyotropic liquid crystal (LC) phase in aqueous dispersions at relatively low concentrations. Under a remarkably wide range of shear rates, we report hitherto unobserved shear-induced polarized light image patterns, a Maltese cross combined with shear banding, recorded in real time and in situ during rheological measurements. This is shown to be a result of elastic flow instabilities that manifest as a helical flow in alternating bands of left- and right-handed helices, arising from a combination of shear flow and Taylor-type vortex flow. The instability is observed for LCs formed from large aspect ratio GO particles owing to their unique viscoelastic properties, but not for smaller aspect ratio particles. This phenomenon coincides with rheopecty and anomalous small-angle X-ray scattering patterns under shear flow, which confirm the instabilities. The results presented here could lead to advanced control over macroscopic periodic alignment in technologically relevant dispersions of two-dimensional material particles.

Experimental determination and modeling of flow curves of xanthan gum solutions over a large range of shear rates

AbstractThe viscosities of solutions formulated with xanthan gum and xanthan gum with whey protein isolates are experimentally characterized and modeled over a wide range of shear rates [10−3to 105s−1]. As shown by numerous studies [1, 2], the generation of vortices in the cone-plate geometry is making viscosity measurements beyond a certain shear rate unreliable. In the present work, an innovative technique, based on microfluidics and developed by the company Formulaction, has been employed to extend to high shear rates, the viscosity flow curve obtained with a rotational rheometer. The main highlights of this study are firstly, to propose a scaling law for the inertial transition in the cone-plate geometry for different diameters and angles through the determination of the maximum shear rate at which one can expect a true viscosity value. Secondly, the high shear rate measurements allow the determination of the second Newtonian plateau for these solutions thanks to the Williams-Carreau model. An attempt for the second plateau modeling is proposed following the concept of an intrinsic viscosity in the high shear equilibrium. In the same way, other fitted parameters from the Williams-Carreau law are modeled as a function of the polymer concentration. This procedure allows to provide a predictive model for the rheological behavior of xanthan gum-based solutions used in high shear processes like high pressure homogenization, emulsification, foaming, microfluidics, etc in food, pharmaceutical or cosmetics applications.

Exploring shear-induced segregation in controlled-velocity granular flows

Particle segregation in geophysical and industrial granular flows is typically driven by gravity and shear. While gravity-induced segregation is relatively well understood, shear-induced segregation is not. In particular, what controls segregation in the absence of gravity and the interplay between shearand gravity-driven segregation remain unclear. Here, we explore the shear-induced segregation force on an intruder particle in controlled-velocity granular flows where the shear profile is systematically varied. The shear-induced segregation force is found to be proportional to the shear rate gradient, which effectively pushes the large intruder from lower to higher shear rate regions. A scaling law is developed for the segregation force that is accurate over a wide range of overburden pressures and shear rates, and hence inertial numbers.

IDENTIFICATION OF RHEOLOGICAL PROPERTIES OF POLY(ETHYLENE OXIDE) – WATER SOLUTIONS

In the paper results of investigations of rheological properties for selected PEO-water solutions are presented. On the basis of measurements, carried out with use of rotational viscosimeter values of shear stresses were determined in the relatively wide range of shear rates. Rheological curves were described by the Ostwald de Waele model (or so-called power-law). The model coefficients such as the fluid consistency coefficient k and the flow behavior index n were determined using Levenberg−Marquardt algorithm for nonlinear estimation. The influence of temperature on properties and behavior examined non-Newtonian fluids was also determined. Results were processed in the curve shift parameter at. Experiments shown a significant effect of poly(ethylene oxide) concentration cPEO on rheological properties of examined solutions. For the lowest concentration (cPEO=1.2%) solutions exhibited properties similar to Newtonian fluids with values of n close to 1. With increasing of PEO concentration in water (cPEO=2.4-4.8%), solutions exhibited properties as non - Newtonian fluids, pseudoplastic, without yield limit. In these cases values of n were below unity and for the highest concentration (cPEO=4.8%) belonged to the range of n=0.5694-0.7536, depending on the temperature. Results of investigations can be used during numerical simulations, design and optimization of industrial equipment, working with fluids of this kind, including mixing vessels, columns or heat exchangers.

Development of Viscosified Acid-Surfactant Solutions for Oilfield Applications: Rheological Properties

Abstract Viscosified acids are desired in several oilfield applications such as in acid diversion and acid fracturing operations. The study aimed to delineate the rheological properties of a novel amine type surfactant and viscosified acid-surfactant solutions. The steady shear and dynamic rheological properties were evaluated by varying the surfactant, acid, and salt concentration. Such a study is required to gauge the suitability of the viscosifying agent in acid stimulation jobs. The surfactant solutions without acid showed shear-thinning behavior, whereas those with acid showed a Newtonian plateau over a wide shear rate range before undergoing shear thinning. This means that over a wide shear rate range, the acid-surfactant solutions become independent of applied shear. At low shear rates, the viscosity of the surfactant was higher compared with the surfactant-acid solution. However, at high shear rates, the viscosity of the surfactant was lower compared with the viscosity of the surfactant-acid solution. There was an optimal salt concentration that improved the viscosity and elasticity of the acid-surfactant solutions. Thus, the rheology of the surfactant solution can be improved by adding both acid and salt. The elastic properties of acid-surfactant solutions were also better compared with the elastic properties of pure surfactant. The addition of acid improved the elastic properties of the surfactant solutions. Constant viscosity over a range of shear rate is a suitable application for acid fracturing operations in which the acid leak-off will be minimal due to the high viscosity. Also, brines in most of the carbonate formation consist of high loading of calcium chloride which was found to have a positive effect on the viscosity. Increasing the calcium chloride leads to an increase in viscosity, and then subsequently decreases the viscosity. This shows that the acid and salt concentration plays a role in modifying the rheological properties of the surfactant solutions.

An Integrated Detection Method for Flow Viscosity Measurements in Microdevices.

Point-of-care devices can analyze or characterize a sample in a short time. New technologies in medical science seek integrations of different measurement techniques for a complete analysis. This study describes the fabrication method, tests, and results of microtechnology as an approach for an integrated rheometer. The portable device measured the average flow velocity to calculate its viscosity. The whole system encompasses a microdevice integrated to a data acquisition system powered by USB and controlled by full custom software. As a result, we obtained an easy-to-handle and fabricate hand-held microrheometer. The device was tested using Newtonian fluids such as Mili-Q water, an aqueous solution of Ethylene-glycol at 40% and 25% and Non-Newtonian blood samples. The whole device can provide the non-linear viscosity of a 0.08ml blood sample in less than 30 seconds, in a wide range of shear rate with an accuracy of 93%. More importantly, due to its detection method and simplicity, it can be enclosed within almost any fluidic microsystem, including biomedical applications.

Measurement and prediction of kinematic viscosity for linear ethers.

Using the methods of equilibrium and non-equilibrium molecular dynamics alongside capillary viscometer experiments, we explore differences between united and all-atom models of a series of linear ethers. The models are based on two transferable force fields, and changes in viscosity and diffusion are studied across a wide range of temperatures and shear rates. We analyze diffusivity and viscosity data by means of the rotational relaxation time and Arrhenius equation. Rotational relaxation times are calculated explicitly from the ether chain's end-to-end vectors, and self-diffusion values are calculated from the mean square displacement. We find an increase in orientational alignment as temperature drops in both models and consistent differences in activation energies across the models and experiment. A clear relationship is observed between viscosity, rotational relaxation time, and diffusion time. These time constants also impact the reliability of the viscosity value determined by the Green-Kubo method. We also study the trends in zero-shear viscosity as chain length increases and force field performance relative to experiment as this length changes.

Investigation on the effects of AlOOH nanoparticles on sodium dodecylbenzenesulfonate stabilized o/w emulsion stability for EOR

Emulisons stabilized by surfactants have been used in enhanced oil recovery (EOR) for effective profile control and displacement, whereas the lack of long-term stability especially under harsh reservoir conditions limited their wide application. In this study, Pickering emulsions stabilized by sodium dodecylbenzenesulfonate (SDBS) and anisotropic slice-like AlOOH nanoparticles were systematically studied. The adsorption of SDBS on AlOOH nanoparticles was confirmed by the measurements of zeta potential and Fourier Transform Infrared (FTIR) spectra. The three-phase contact angle tests were conducted to explore the reason for the double phase inversion of the AlOOH/SDBS stabilized emulsions from o/w to w/o and back to o/w again. The optical microscopy images verified the adsorption mechanism of SDBS on AlOOH nanoparticles at the oil/water interface. It was found that the three-dimensional network structure formed by the micro-flocculated modified AlOOH nanoparticles could prevent coalescence and phase separation, resulting in the enhanced stability of the emulsion. The AlOOH/SDBS stabilized emulsion showed the super tolerances in a wide range of shear rates, temperature and electrolyte concentrations. The core flooding tests and microscopic visualization flooding experiments demonstrated that the AlOOH/SDBS stabilized emulsions significantly improved the tertiary oil recovery (33 % of IOIP) via the enhanced displacement and sweep efficiencies. The present study provides a typical Pickering emulsion with great stability under harsh reservoir conditions for EOR.

Development of New Rheological Models for Class G Cement with Nanoclay as an Additive Using Machine Learning Techniques.

The rheology of the oil well cement plays a pivotal role in the cement placement. Accurate prediction of cement rheological parameters helps to monitor the durability and pumpability of the cement slurry. In this study, an artificial neural network is used to develop different models for the prediction of various rheological parameters such as shear stress, apparent viscosity, plastic viscosity, and yield point of a class G cement slurry with nanoclay as an additive. An extensive experimental study was conducted to generate enough data set for the training of artificial intelligence models. The class G oil well cement slurries were prepared by fixing the water–cement ratio to 0.44 and adding organically modified nanoclays as a strength enhancer. The rheological properties of the oil well cement slurries were investigated at a wide range of temperatures (37 ≤ T ≤ 90 °C) and shear rates (5 ≤ γ ≤ 500 s–1). Experimental data generated were used for the training of feed-forward neural networks. The predicted values of the rheological properties from the trained model showed a good agreement when compared with the experimental values. The average absolute percentage error was less than 5% in both training and validation phases of modeling. A trend analysis was carried out to ensure that the proposed models can define the underlying physics. From the validation and the trend analysis, it was found that the new models can be used to predict cement rheological properties within the range of data set on which the models were trained. The proposed models are independent of laboratory-dependent variables and can give quick and real-time values of the rheological parameters.

Hydrodynamic forces on a clean spherical bubble translating in a wall-bounded linear shear flow

The three-dimensional flow around a spherical clean bubble translating steadily in a wall-bounded linear shear flow is studied numerically. The present work is concerned with the drag and lift forces experienced by the bubble over a wide range of Reynolds number (0.1 ≤ Re ≤ 103, Re being based on the bubble diameter and relative velocity with respect to the ambient fluid), wall distance (1.5 ≤ LR ≤ 8, LR being the distance from the bubble center to the wall normalized by the bubble radius), and relative shear rate (−0.5 ≤ Sr ≤ 0.5, Sr being the ratio between the velocity difference across the bubble and the relative velocity). Based on the above range of parameters, situations where the bubble is repelled from or attracted to the wall are both covered. The flow structure and vorticity field are analyzed to obtain qualitative insight into the interaction mechanisms at work. The drag and lift forces are computed as well. Their variations agree well with theoretical predictions available in the limit of low-but-finite Reynolds number and, when the fluid is at rest, in the potential flow limit. Numerical results and analytical expressions are combined to provide accurate semi-empirical expressions for the drag and lift forces at arbitrary Reynolds number and separation distance.

Addendum to: Exploring Hidden Local Ordering in Microemulsions with a Weak Directive Second Order Parameter

In a recent publication, my group discussed a directive second order parameter that hypothetically could form micrometer large structures that influence the rheological behavior of a bicontinuous microemulsion. For this, the viscosities of two microemulsions with the non-ionic surfactants C10E4 and C8E3 were determined over the wide frequency and shear rate range. Contrarily to our previous publications there are no elevated viscosities towards slowest motions of the rheometer. Thus, no micrometer large structures form in microemulsions. However, we argue and confirm that there are compartments with the size of several correlation lengths. This finding supports the development of a directional order parameter in microemulsions.